Said RFID tags are known from the prior art, and are generally used to store data or for object identification. For example, consumer articles are equipped with such tags in order to electronically reveal the price, ingredients, instructions for use and the like in a simple way. The invention therefore relates generally to data carriers which can be written to and read from wirelessly.
The aforementioned RFID tags are in general comparatively small, and are adhesively bonded onto an object or are directly contained in it. With the aid of an antenna which is usually integrated in the RFID tag, it is possible to communicate with a communication station, a so-called “reader”. Distinction is also generally made between active and passive RFID tags, passive RFID tags not having their own current or energy supply. In this case, with the aid of the integrated antenna, the RFID tag is supplied with energy which is drawn from the electromagnetic field radiated by the communication station or transceiving device. In this way, it is possible to read data from a passive transponder or write data to it.
In order to achieve an adequate energy supply for the aforementioned transponder, however, the antenna of the communication station must provide a correspondingly strong field. There are furthermore systems in which a multiplicity of such transponders, or objects provided with such transponders, are arranged in a very narrow space so that, according to the position of the transponders and/or objects provided with them, the antenna of the communication system must also be matched to the position of the transponders.
In order to pick up a multiplicity of transponders simultaneously, according to the state of the art it is also possible to use a common antenna. Normally, the antenna then simply envelops the read/write regions for the transponders. Owing to the larger dimensions of an antenna for a multitude of transponders compared with an antenna for a single transponder, however, the field strength in areas further away from the antenna conductor decreases strongly so that communication between the communication station and the transponders is not possible there, or is possible only to a limited extent.
The aforementioned problem also arises in the event that a multiplicity of transponders are arranged essentially along a line, with a corresponding design of an antenna having a length-to-width ratio of much more than 1. The mutually parallel antenna conductor sections which extend in the longitudinal direction primarily contribute to the formation of the field in this case, and the antenna conductor sections extending transversely thereto in the width direction contribute less. With such an antenna, therefore, it must also be assumed that there is not an adequately strong electromagnetic field in the central region to offer an adequate energy supply for normal transponders when complying with conventional spacings.
In the case of antennas for a multitude of transponders, it is therefore necessary to ensure either that a stronger energy supply is applied to the antenna, which in turn entails larger conductor cross sections, or that the transponders or products equipped with them are placed closer to the antenna. However, any reduction of the distance between the antenna and the transponder is often restricted by design conditions, when such transponders are integrated in a product equipped with them.
In order to achieve sufficiently large fields, as an alternative, a multiplicity of antennas may for example be arranged in a row or line form corresponding to the number of transponder positions, although such a structure is disadvantageous owing to the increased multiplicity of terminals and supply or connection lines to the individual antennas, and entails increased cost and design outlay.